CASSCF study of bonding in NiCO and FeCO

Abstract

A series of CASSCF calculations were performed on the ground states of NiCO and FeCO. The contributions of the σ/π interactions are checked by examining the validity of the CASSC calculation to describe the molecule with a particular choice of the active space. The calculation results substantiate that the stability of MCO is determined by a balance between π donation from the metal 3dπ to the CO 2π and repulsion between the metal σ electrons and the CO 5σ lone pair and, at the same time, emphasizes the importance of the synergistic σ/π interactions between the metal and the CO group. The relative importance of σ/π interactions depends on the nature of the metal. In the case of NiCO, it is the π donation from Ni 3dπ to CO 2π that makes the largest contribution to the formation of the NiCO bond, while in the case of FeCO, it is the correlation of σ electrons that holds the metal and CO together. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 221–231, 1999